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thread fit problem

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a63mariner

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#1
I machined 6 units each consisting of a male screw and female nut 2"-10, 60 degree thread. I used a carbide insert tool. The first 5 units fit together satisfactorially, screwing the male into the nut from EITHER end. The sixth unit fits together from one end easily by hand, but when I reverse the nut and attempt to install the male screw from the OPPOSITE end, it jams about 5/8" in. Material is 10L14. nut OD is 3" open both ends. Male threads are 21/2" long, with a 21/2" OD cap or bolt head. I intendto use these to raise my bench top lathe up to a more comfortable heigth. Any suggestions on fixing the problem would be greatly appreciated.
Thanks in advance, Ken
 

4gsr

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#2
Thread bore should be in the range of 1.913 down to 1.892. Any smaller can cause issues.
For a class 2 thread, the minimum clearance between the threads is about .002". To me that is too close and I would increase the P.D. of the nut thread to get more running clearance. Also, check your threading tool, may have worn or nicked an edge. Last, how many spring passes did you make?
 

a63mariner

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#3
Thanks for your answer. I'm within your spec. for the nut bore. the tool looks good under a magnifying glass. I took several spring passes during threading, and when doing so I would take a second or third pass until no metal was being removed. What puzzles me is why the nut fits in only one direction.I threaded to a depth of approx. .065, Trying the male thread until I got a good running fit. I don't intend for these units to be interchangeable.
Ken
 

whitmore

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#4
I machined 6 units each consisting of a male screw and female nut ...but when I reverse the nut and attempt to install the male screw from the OPPOSITE end, it jams about 5/8" in
That could mean that the tool wasn't completely perpendicular to the work axis, instead of being
30 degrees each side, it made 29.5 and 30.5 degree flanks. Slight cocking of the toolholder
in the middle of turning could do it, especially if the internal thread was also slightly off-axis.

Thread symmetry can be a useful parameter to break: this caught my eye a few weeks back
Vibration-proof threads
 

kd4gij

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#5
We make inboard boat shafts where I work. We use brass nuts from 3/4" to 2 1/2" most of the nuts we get in will only go on 1 way. Have to run a tap through them to get them to go both ways.
 

Technical Ted

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#6
This may be way off, but is it possible that your lead screw is worn where you are threading these pieces and they will fit together in the same direction they were both threaded from (with this slight inaccuracy in the lead) but when turning one of the pieces around there is an interference because the lead is slightly off???

Edit add: or the ways are worn and the pitch diameter varies in opposite directions when one of the pieces is reversed?

Wild guess I know, but might be worth a thought,
Ted
 

a63mariner

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#7
Thanks for your answer. I'm within your spec. for the nut bore. the tool looks good under a magnifying glass. I took several spring passes during threading, and when doing so I would take a second or third pass until no metal was being removed. What puzzles me is why the nut fits in only one direction.I threaded to a depth of approx. .065, Trying the male thread until I got a good running fit. I don't intend for these units to be interchangeable.
Ken
I checked tool alingment with my magnifiers on, and it's fine. I think that wear on the lead screw or the ways would affect ALL six pieces. Only the sixth piece is causing problems. I tried to realign the tool with the internal thread, in order to cut it a little deeper, but couldn't see well enough into the bore. May try to recut the OD thread. Sprial thread article was interesting.
thanks to all, Ken
 
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